Process for the thermal decoking of cracked gas coolers

Abstract

A process for the thermal decoking of cracked gas coolers for the indirect cooling, by means of water, of ethylene-containing cracked gases which are obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tube cracking furnace, at cracked gas exit temperature of above 750° C., in which, instead of a heated steam/air mixture, heated air, without steam, is passed through the cracked gas cooled tubes which are to be decoked.

I claim: 
     
       1. A process for the thermal decoking of cracked gas coolers for the indirect cooling, by means of water, of ethylene-containing cracked gases which are obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tube cracking furnace at cracked gas exit temperatures of above 750° C., which process comprises: stopping the introduction of the hydrocarbon to be cracked to the cracking furnace, and passing a steam/air mixture through the indirectly heated cracking tubes of the furnace and at the same time through the downstream cracked gas cooler and, after completion of decoking of the cracking tubes of the furnace, stopping the supply of steam and thereafter passing only heated air or an air/oxygen mixture through the indirectly heated cracking tubes of the tube cracking furnace in such an amount that the ratio of the hourly weight throughput of heated air or heated air/oxygen mixture to the hourly throughput of hydrocarbon during thermal cracking is from 0.1 to 3, such air or air/oxygen mixture being heated to temperatures of from 600°to 1,100° C. and passing the heated air or air/oxygen mixture through the cracked gas cooler tubes which are to be decoked for a sufficient period to substantially decoke said cooler tubes and maintaining at the same time a steam pressure of at least 90 bar on the boiling water side of the cracked gas cooler. 
     
     
       2. The process of claim 1, wherein the cracked gas cooler is decoked to the point that the exit temperature of the cracked gas from the cooler corresponds to the initial value of the exit temperature when the cooler is first put into operation, or is put into operation after mechanical cleaning of the cooler.